The high power interference regime produced during Electronic Warfare (EW) operations creates a challenging electromagnetic environment for robust communication. This undesirable situation is exacerbated by the presence of intentional interferers, such as those present in the theater of war. Accordingly, communication and data link transceivers should ideally be able to operate in the presence of high-power, adjacent-channel interference. However, achieving the isolation necessary for adjacent channel operation requires layered interference mitigation techniques, including in both the digital and analog domains. Unfortunately, in spite of significant advancements of technology in digital domain, the analog domain has not improved significantly. Therefore, despite the advancements of digital technologies, there is a pressing need for RF signal conditioning and ant-jamming filter systems.
In the digital domain, components such as DSPs (Digital Signal Processors) and FPGAs (Field-Programmable Gate Arrays) have matured in recent decades. Such devices perform very effective signal conditioning, detection and estimation, typically after the signal has been filtered with a suitable band selection filter. However, the band selection itself in the analog domain has not kept pace with the digital advancements, especially in the transition RF range between lumped and distributed technologies (e.g., 10 MHz to 4 GHz). For C4ISR (Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance) operation, in particular, systems must be able to receive a weak signal in the presence of a strong interfering signal and still achieve optimal sensitivity above the thermal noise background. To this end the transceiver ideally will have a dynamic range,Dr, of: Dr=PI/(SNBW)=PI/kT BW),where: BW is the bandwidth, PI is the interference power, and SN=kT is the noise floor (i.e., noise power per degree of freedom). Therefore, for a given bandwidth of BW, a higher power in the bandwidth of operation translates to higher requirement for dynamic range, Dr. This is, however, not feasible given >100 dB of typical power difference between a typical C4ISR signal of interest and the transmit power of cosite transmitters.
To exemplify this, the acceptable power is <1 mW at analog-to-digital converters in almost all advanced radios (10 mW is preferred). Even a commercial 3G cell phone's own transmitted signal of around 300 mW impinges on the received signal, requiring preselect filters and diplexers. Unfortunately, the existing compact preselect filters have fixed band frequencies (and, have high losses), while, solutions that demand low loss (e.g., in radar applications) are bulky and still non-tunable. Therefore, there is demand for low-loss solutions that are both compact and tunable.
Patent application Ser. No. 12/960,363, responded to this demand using a band-stop filter component concept.